/*
 * Copyright 2012-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package cn.springcloud.gray.bean.convert;

import java.util.Collection;
import java.util.Collections;
import java.util.Set;
import java.util.stream.Collectors;

import org.springframework.core.convert.ConversionService;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;

/**
 * Converts a Collection to a delimited String.
 *
 * @author Phillip Webb
 */
final class CollectionToDelimitedStringConverter implements ConditionalGenericConverter {

    private final ConversionService conversionService;

    CollectionToDelimitedStringConverter(ConversionService conversionService) {
        this.conversionService = conversionService;
    }

    @Override
    public Set<ConvertiblePair> getConvertibleTypes() {
        return Collections.singleton(new ConvertiblePair(Collection.class, String.class));
    }

    @Override
    public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
        TypeDescriptor sourceElementType = sourceType.getElementTypeDescriptor();
        if (targetType == null || sourceElementType == null) {
            return true;
        }
        if (this.conversionService.canConvert(sourceElementType, targetType)
                || sourceElementType.getType().isAssignableFrom(targetType.getType())) {
            return true;
        }
        return false;
    }

    @Override
    public Object convert(Object source, TypeDescriptor sourceType,
                          TypeDescriptor targetType) {
        if (source == null) {
            return null;
        }
        Collection<?> sourceCollection = (Collection<?>) source;
        return convert(sourceCollection, sourceType, targetType);
    }

    private Object convert(Collection<?> source, TypeDescriptor sourceType,
                           TypeDescriptor targetType) {
        if (source.isEmpty()) {
            return "";
        }
        return source.stream()
                .map((element) -> convertElement(element, sourceType, targetType))
                .collect(Collectors.joining(getDelimiter(sourceType)));
    }

    private CharSequence getDelimiter(TypeDescriptor sourceType) {
        Delimiter annotation = sourceType.getAnnotation(Delimiter.class);
        return (annotation != null) ? annotation.value() : ",";
    }

    private String convertElement(Object element, TypeDescriptor sourceType,
                                  TypeDescriptor targetType) {
        return String.valueOf(this.conversionService.convert(element,
                sourceType.elementTypeDescriptor(element), targetType));
    }

}
